1. Field of the Invention
The present invention relates to an energy storage device, e.g., for a photovoltaic system, a control device, and a method for operating an energy storage device.
2. Description of the Related Art
In an energy storage device for photovoltaic systems, the same type of batteries, for example multiple structurally identical lead gel accumulators or multiple structurally identical lithium-ion accumulators of the same type, are typically used.
The requirements for the energy stores of the energy storage device, such as the cycle stability and calendar service life, are crucial for the cost of the energy storage device. For example, an energy store of an energy storage device in a photovoltaic system must tolerate a fairly long period of a high state of charge in the summer, and of a low state of charge in the winter. In addition, consumption-related microcycles influence the service life of the energy stores. The higher the cycle stability and the longer the calendar service life, the higher the cost of the energy stores.
Published German patent application document DE 10 2010 019 268 A1 describes a device in which the battery bank is formed by a plurality of batteries or battery groups connected in series. A predetermined number of the batteries or battery groups electrically situated at the positive side of the photovoltaic system are each provided with a tap or tapping terminal. One of the taps is selected according to the level of a desired discharge current, and is connected to the positive input terminal of the inverter via an isolating switch.